This invention provides a low cost means for achieving affordable solar energy by greatly reducing the cost of solar concentrators which increase (concentrate) the density of solar energy incident on the solar energy converter. A limiting factor in the utilization of solar energy is the high cost of energy converters such as photovoltaic cells. For example, for the purpose of generating electricity, a large area of expensive solar cells may be replaced by a small area of high-grade photovoltaic solar cells operating in conjunction with inexpensive intelligent micro-optics of this invention. Thus the instant invention can contribute to the goal of achieving environmentally clean energy on a large enough scale to be competitive with conventional energy sources.
The rotatable elements of this inventions are balls and cylinders. As derived in U.S. Pat. No. 6,612,705 of which the inventor of this instant invention is the co-inventor, balls in a square array have a packing fraction of 0.785 and 0.907 in an hexagonal array. Balls have an advantage over cylinders in that they can operate in either a single-axis or two-axis tracking mode. Cylinders have an advantage over balls in that they can have a packing fraction of nearly 1, but they are limited to a single-axis tracking mode.
The presence of rotatable mirrors in a solar concentrator presents either a dilemma or an opportunity with respect to the basic nature of the alignment implementation. Mirrors are normally made of a conductive metallic coating. In an applied electrostatic field, E, a dipole moment is induced in the metallic conducting material of the micro-mirrors because the charge distributes itself so as to produce a field free region inside the conductor. To internally cancel the applied field E, free electrons move to the end of each conducting mirror antiparallel to the direction of E, leaving positive charge at the end that is parallel to the direction of E. Another way to think of this in equilibrium is that a good conductor cannot long support a voltage difference across it without a current source. An induced electrostatic dipole in a conductor in an electrostatic field is somewhat analogous to an induced magnetic dipole in a pivoted ferromagnetic material in a magnetic field, which effect most people have experienced. When pivoted, a high aspect ratio (length to diameter ratio) ferromagnetic material rotates to align itself parallel to an external magnetic field.
If alignment is attempted in a conventional manner such as is used in Gyricon displays, the induced polarization electric dipole field presents a dilemma since it is perpendicular to the zeta potential produced dipole field and the net vector is in neither direction. The “zeta potential,” is the net surface and volume charge that lies within the shear slipping surface resulting from the motion of a body through a liquid. The zeta potential is an electrical potential that exists across the interface of all solids and liquids. It is also known as the electrokinetic potential. The zeta potential produces an electric dipole field when a sphere it is made from two dielectrically different hemispheres due to their interaction with the fluid surrounding it.
One way to eliminate or greatly diminish the effect of the zeta potential is to make the surface of both hemispheres out of the same material. This would be quite difficult for Gyricon displays because they require optically different surfaces e.g. black and white, or e.g. cyan, magenta, and yellow for color mixing. In the instant invention, no problem arises by making both hemispheres out of the same transparent material to eliminate or minimize the zeta potential. In fact this presents an opportunity to both utilize the induced polarization electric dipole field and to have two mirror surfaces. With two mirror surfaces, an option presents itself to use the better surface as the surface that reflects the light, and furthermore to have a standby mirror in each element should one of the mirrors degrade. A permanent electret dipole can be sandwiched between the two induced dipole mirrors to further enhance the dipole field that interacts with the addressable alignment fields.
The topic of the dipole interactions between balls seems not to have been discussed in the Gyricon patents and literature. A heuristic analysis shows that this is not a serious problem. The electric field strength of a dipole, Ed is proportional to 1/r3, where r is the radial distance from the center of the dipole. The energy in the field is proportianal to (Ed)2. Thus the energy of a dipole field varies as 1/r6. The force is proportional to the gradient of the field, and hence varies as 1/r7. With such a rapid fall off of the dipole interaction force, it can generally be made very small compared to the force due to the applied field E, and to the frictional forces that are normally present. Therefore interaction of the dipole field forces between mirrored elements (balls or cylinders) can generally be made negligible.
The 1998 Gyricon U.S. Pat. No. 5,717,515 of Sheridon, entitled “Canted Electric Fields for Addressing a Twisting Ball Display” is exclusively concerned with Displays. There appears to be no mention of any other application than directly viewed Displays, either specifically or by general statement. In this Sheridon patent, no mention is made of a mirror in the gyricon balls, nor is there any mention of specular reflection as would be obtained from a mirror. On the contrary, means are discussed to increase diffuse reflection from the balls so the Gyricon display may easily be observed from all angles. Certainly there is no anticipation of a solar concentrator application, mirrored illumination and projection, solar propulsion assist, or any other micro-mirror application. Furthermore there is no mention of coupling means to the balls other than by means of the zeta potential dipole, or an electret dipole both of which are parallel to the Gyricon axis of symmetry which in the case of black and white balls goes through the vertex of the black hemisphere, the center of the sphere, and the vertex of the white hemisphere. Also there is no mention of an induced polarization electric dipole in the balls. In their dielectric balls there is an inadvertent insignificant induced polarization electric dipole in the dielectric, but it is small compared with the induced polarization electric dipole of the instant invention. Furthermore, it is parallel to the Gyricon axis of symmetry, whereas in the instant invention the induced polarization electric dipole is perpendicular to the axis of symmetry. Thus the application of the same electric field in the instant invention produces an entirely different orientation or alignment than in the Sheridon patent.
This Sheridon patent focuses on emodiments of “segmented electrodes” for Displays only, without mention of other applications, or that their invention may be applied more broadly. Yet, interestingly, some of the claims are quite general. Since claims should be a summary of the invention described in the specification, it appears that such broad claims are not warranted by the specification. Nor do such broad claims seem warranted in view of the prior 1981 Goodrich U.S. Pat. No. 4,261,653, which is also quite specific, and differs considerably from the instant invention.
The instant invention differs substantially from that of Sheridon and from that of Goodrich in the use of: mirrored balls and cylinders; induced polarization electric dipoles in the mirrors with or without permanent dipoles in electrets; the dipole fields being perpendicular to the axis of symmetry (rather than parallel); the use of fragmented wire electrodes to provide greater transparency; and the combination of fragmented wire electrodes and partitoned electrodes to provide greater transparency of the active surface than in the Sheriron patent.
The instant invention is primarily concerned with method and apparatus for the alignment of solar concentrator micro-mirrors. However, it has broader applications wherever mirrors are used for focussing such as for solar propulsion assist, illumination and projection of light, optical switching, etc.